Renal
dysplasia (RD) is
a medical term that refers to improper development of the kidneys
This condition can be inherited (genetic) or acquired. The
genetic form of this disease is found in many breeds, and has
been
widely reported for many in the scientific literature. Sadly
there is no cure, and this disease is potentially fatal.
Supportive treatment including diet may help with the dog’s quality of
life. A veterinarian should be consulted for treatment options.

What are the symptoms
of Renal
Dysplasia?

Often
there are no warning signs and this disease is not apparent until the
kidneys begin to fail. Initially owners may notice signs of
increased urination and drinking. Dogs experiencing end stage renal
failure may have various symptoms including vomiting, weight loss, poor
appetite (anorexia), lethargy, muscle weakness, poor coat, and dilute
urine. Secondary urinary tract infections may occur. The symptoms and
severity of RD are highly variable amongst individuals.

How
is Renal Dysplasia diagnosed?

Since
renal dysplasia is a failure of the kidneys to develop, mature dogs
have kidneys containing fetal tissue types. A biopsy of a small piece
of kidney tissue is done to confirm the diagnosis. Microscopic
examination of the tissue shows underdeveloped glomeruli, compact
clusters of capillaries that filter waste products and excess water
from the blood. The waste is excreted as urine. The percentage of fetal
glomeruli found in the biopsy is predictive of the severity of the
disease. All dog breeds with renal dysplasia have this phenotype.

Renal dysplasia is
not limited
to puppies under the age of 2.

For
many years
the term “juvenile renal dysplasia” has been used to
describe this form
of inherited kidney disease. The mislabeling of renal dysplasia
as
juvenile condition has resulted in confusion about the disease, and
consequently many breeders have assumed that the problem does not exist
in their kennel. The age of onset is highly variable, and kidney
failure from this birth defect can occur at any age, even in dogs that
are up to 10 years of age or beyond. In fact more adults over the
age
of 5 will die from RD than puppies. Ultimately, this disease will
shorten the life of many adults.

A Genetic test for Renal Dysplasia

A genetic test is now available to determine if a dog is at risk for
developing renal dysplasia (1). The results are reported as
“clear”,
meaning that the animal has no copies of a mutant allele, carrier (one
copy of a mutation) or homozygous for mutant alleles (two copies of a
mutation). An animal is at risk to develop RD if they have one or
two
copies of the mutation. Renal dysplasia is inherited as dominant,
meaning that a single copy of a mutation is sufficient to cause
disease. Animals with one or two copies of a mutation may be
clinically normal throughout life, or may develop the disease later
on. Early onset of the disease, which is rare, may show up in
puppies
as early as 4 weeks. This test can be used to separate out cases
that
are inherited rather than acquired. More importantly, the test is a
tool to eliminate the mutations from the breeding stock. Animals that
have a normal biopsy but have the mutation can still pass the disease
on to their offspring.

Unlike a biopsy, the
genetic test cannot predict the severity of the disease.

The
Mode of Inheritance Gives Rise to Highly Variable Pathology.

Renal
dysplasia is inherited with incomplete penetrance. If a mutation
is fully penetrant 100% of the individuals with the mutation will have
the disease. If the penetrance is incomplete, not all individuals
with the mutation will show signs of the disease. In the case of
renal dysplasia, the penetrance is low and only a small percentage of
adults will be clinically affected. The percentage of fetal glomeruli
found in a renal wedge biopsy is highly variable. Some animals will be
clinically normal, but can pass the disease onto their offspring. While
signs of the disease may never show up before an animal dies from
other causes, an estimated 3-5 % of adults with one or two copies of a
mutation could die from end-stage renal failure (1).

The
lifespan of an animal is dependant on the severity of the defect at
birth. Animals with a moderate to severe defect may have no
symptoms until the renal function is diminished by 70-75%, and
this can take years to develop. At some point the kidney will no
longer be able to compensate for the diminished function.

SummaryRenal
dysplasia in dogs is inherited in many breeds, has a wide range of
clinical symptoms and can manifest at any age. Diagnosis of RD is
difficult, and the mode of inheritance is complex.

A genetic
test is now available to eliminate this from breeding stock. For
more information on genetic testing and breeding strategies visit:DOGenes.com